The invention relates to an over-center knuckle-joint hinge having a supporting-wall member and a door member which are joined to one another by a knuckle-joint mechanism formed by two arms coupled together in their central area, one of the extremities of the arms being articulated to the supporting-wall member in the one case and to the door member in the other, while the other end in each case is coupled to the other member either in a sliding guide or indirectly through a link, and having an over-center mechanism resiliently urging the hinge into the end position of the hinge, at least in the vicinity of the closed position, the closing spring of said over-center mechanism being disposed and supported at the arm linked to the supporting-wall member, while its second end is supported directly or indirectly against a counter-surface which during the hinge pivoting action changes its spatial position relative to this spring end from the one end position to the other such that the spring undergoes a maximum deflection in an intermediate position.
In a known knuckle-joint hinge (German Offenlegungsschrift No. 2,219,616), in which the arm articulated to the door member is coupled indirectly to the supporting-wall member through a link, a closing spring bent in a U-shape is so disposed on this link that its bend passes around the pivot pin which joins the link to the arm. One limb of the spring is supported against the link, while the other limb presses against a guiding path which is provided on the supporting-wall member and is so constructed that the desired closing action is achieved. Such a construction of the closing or over-center mechanism, however, is practical only in knuckle-joint hinges in which the above-mentioned link is present. In practice, however, knuckle-joint hinges are also frequently used in which the arm articulated to the door member is coupled directly to the supporting-wall member by a slide-like guide (e.g., German Pat. No. 1,958,983). In this case, a certain required movement of the hinge can be achieved most simply by providing an appropriate curve in the slide groove, and yet any over-center mechanism that might have to be provided has to be provided in the vicinity of the arms of the knuckle joint, and this is difficult, particularly on account of the little space that is available in the closed position of the hinge. In a hinge of the initially described kind which is provided with an over-center mechanish (German Offenlegungsschrift No. 2,323,412), the closing spring that is mounted on one of the arms is in the form of a curved leaf spring which cooperates with a roller disposed on a projection of a link connecting the arm to the door member. This design requires a relatively great amount of space, so that the arm holding the leaf spring, as well as the link provided with the roller, has undesirably great dimensions and therefore give the hinge a clumsy appearance.